Peroxycarboxylic acids (i.e. peracids, such as peracetic acid) fall into the chemical category of “organic peroxides” which in turn are classified as self-reactive, self-heating substances. Self-reactive substances are strictly regulated by the US Department of Transportation (DOT) following the guidance of the UN Committee for the Transport of Dangerous Goods (TDG). Like the US DOT most local and national governments strictly observe the UN TDG guidance thus making their “guidance” essentially a world wide requirement. These guidances may be found in the UN document known as the “orange book,” titled Recommendations on the Transport Of Dangerous Goods, 5th revised edition, 2009.
The concern about self-heating substances is that most decomposition processes accelerate as temperature rises and usually exponentially. A self-heating process producing heat faster than it can cool is the definition of a runaway reaction. In the case of organic peroxides the runaway reaction is accompanied by the generation of large volumes of gas and therefore poses an extreme explosion risk. It is therefore an absolute requirement for purposes of safety, with the ancillary benefit of improving both shelf-life and quality, that the heat generating rate of the organic peroxide containing product not exceed the cooling rate of the package. In addition, since the cooling rates decrease with increased volume, these self-heating rates limit a commercial package size which in turn limits commercial opportunities. If for example a product falls into UN category 5.2 (D), as do some organic peroxides, they may not be sold in packages with a volume greater than 50 kg. For a customer consuming hundreds of kilograms of product per day such a limitation may be unacceptable.
In summary there are two aspects (and two sets of tests) of a prospective “self-reactive substance” to address, the first involves the characterization of the chemical (5.2 A, B, C, D, E, F or G) and the second set of tests assesses the chemistry in the proposed package of commerce. By testing the chemistry in the proposed commercial package the heat loss characteristics as well as the heat generating characteristics are assessed at various “ambient” temperatures. The minimum ambient temperature at which the chemistry self heats to exceed the ambient by at least 6 degrees Celsius is defined as the “Self Accelerating Decomposition Temperature” (SADT). Restrictions on shipping, storage (i.e. refrigeration requirements) come therefore not just from the classification test but also the SADT. If for example the package has an SADT<45 degrees Celsius refrigeration is required. A requirement of refrigeration, like classification can severely restrict commercial opportunities.
Various factors impact the transportation and/or storage risk and therefore a specific product is required to be transported below its SADT. For example, the larger a container, the lower its surface-to-volume ratio will be, resulting in less transmittal of heat to the surroundings container when undergoing thermal decomposition and a reduction in the SADT. This increases the risk of storing and transporting peroxycarboxylic acid compounds susceptible to exothermic decomposition within large containers. This hazard can be minimized by storing and transporting such compositions in containers having been diluted with one or more liquids. The diluted peroxycarboxylic acids can also be formulated into suspensions, emulsions, or solutions. Aqueous emulsions or suspensions are generally considered safer formulations, because the active peroxide is dispersed in the water phase (e.g. suitable for removing heat of decomposing peroxide molecules, such as by convection and/or evaporation). Thus commercially-available peroxycarboxylic acids are usually sold in an equilibrium solution, containing the corresponding carboxylic acid to the peroxycarboxylic acid, hydrogen peroxide and water.
Storage and/or transportation containers may also be made of substances that can withstand the pressures resulting from the inevitable gaseous decay products but they must also be made of inert or semi-inert materials. For aqueous organic peroxides the most common containers are made of high density polyethylene or polypropylene fitted with vented closures. Corrosion sensitive steel for example is not used as it will contaminate the product with transition metal ions such as Fe3+ which are catalytical decay accelerants for most organic peroxides. Packages range in size from several gram bottles to bulk storage tanks depending largely on their classification and their package-specific SADTs. Still further, peroxycarboxylic acid compositions can be transported under refrigeration.
In non-refrigeration transport and storage it becomes almost an absolute necessity to employ transition metal chelators or “stabilizers” to both elevate the SADTs as well as to maximize the shelf-life and quality of organic peroxides. These stabilizers can be used in peroxycarboxylic acid compositions to stabilize the compositions. For example, phosphonate based stabilizers, such as phosphoric acid and salts, pyrophosphoric acid and salts and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) and salts, are the most commonly used stabilizers in peroxycarboxylic acid compositions. When used individually at a sufficient concentration, these stabilizers can significantly improve the stability of the peroxycarboxylic acid compositions, and for the conventional (i.e. non-highly acidic) peroxycarboxylic acid compositions, the stability profile achieved with these stabilizers allows for the commercial transportation and use of these compositions. However, for peroxycarboxylic acid compositions with highly acidic formulations, including for example using strong mineral acids, these stabilizers' efficacy is greatly reduced, in many instances the efficacy is essentially non-existant.
Accordingly, it is an objective of the claimed invention to develop stabilized peroxycarboxylic acid compositions having reduced storage and/or transportation hazards.
In a particular aspect, the stabilized compositions which overcome the challenges associated with the SADT of conventional peroxycarboxylic acid compositions. In addition these stabilizer compositions may even affect the DOT classification, providing in some cases an exemption from the typical UN “5.2” class for organic peracids to the reduced risk “5.1” classification.
A further object of the invention is to provide a stabilized peroxycarboxylic acid composition suitable for storage and/or transport at temperatures of at least 50° C. without presenting SADT hazards.
A still further object of the invention is to provide a stabilized, highly acidic, mixed peroxycarboxylic acid composition utilizing a unique peracid stabilizing agent.
Other objects, advantages and features of the present invention will become apparent from the following specification taken in conjunction with the accompanying drawings.